The paper label industry requires aqueous emulsion based pressure sensitive adhesives (PSA) which will provide good adhesion and tack performance at 0.degree. to 20.degree. F. (-18.degree. to -7.degree. C.) on various substrates. It is also desired that the PSAs be suitable, with aggressive adhesion, at 40.degree. F. to 100.degree. F. (4.degree. to 38.degree. C.). The types of adhesives meeting these requirements are called "all temperature" PSA's.
Generally, acrylic PSA's have been best suited for these applications due to their low Tg and relative cost/performance ratios. However, to provide adequate performance at low temperatures, the acrylic adhesives are generally designed to have very low Tg's (less than -50.degree. C.) and possess significant low molecular weight fractions. This combination of features generally results in poor room temperature performance and low cohesive strength which contributes to label converting/processing difficulties.
An alternative method to that of designing the acrylic adhesive with the above features is to formulate an acrylic PSA which originally had good room temperature performance. Generally, compatible plasticizing agents are introduced to reduce the Tg of the acrylic polymer and promote flow during low temperature applications. This approach, however, also tends to diminish room temperature performance and significantly decreases cohesive strength. Also, because plasticizers are generally very low in molecular weight, they may be fugitive resulting in a change in PSA performance with time.
The PSA industry requires a non-fugitive, easily introduced additive to an aqueous acrylic polymer emulsion that will promote reduced temperature adhesive performance without significantly diminishing room temperature performance or cohesive strength.
Japanese Patent Publn. No. 1974-23,813 discloses pressure sensitive bonding agents for use at low temperatures made of compositions comprising at least one nonionic surface active agent that contains an ethylene oxide group as its hydrophilic component and at least one copolymer. Actual Example 1 shows a mixture of 180 weight parts of a 50 wt % aqueous emulsion of an ethyl acrylate/vinyl acetate/methacrylic acid copolymer blended with 100 weight parts of polyoxyethylene nonylphenyl ether (HLB=13).